The iOS 18.2 update allows users to direct Siri queries to ChatGPT, enhancing AI capabilities on iPhones. To activate this feature, users can say "Siri, ask ChatGPT" or set it up through the Settings app. ChatGPT can handle complex tasks beyond Apple Intelligence, but may need device information for certain queries. Users can control data sharing and confirm requests, making it simple to switch between Siri and ChatGPT for queries.